1. Field of the Invention
This invention relates in general to multi-poise condensing furnaces and, in particular, to a method and apparatus for preventing splashing condensate in the collector box of a multi-poise condensing furnace from activating a safety pressure switch connected to the collector box.
2. Discussion of the Background Art
The residential heating industry has benefitted with the advent of multi-poise condensing gas furnaces. These furnaces typically include a primary heat exchanger positioned adjacent a secondary or condensing heat exchanger. A blower provides circulating air flow over the heat exchangers to produce heated air that may be directed and channeled to a desired location. The design of the multi-poise condensing furnace is optimized so that the furnace may be installed with any one of four different physical orientations while being capable of operating properly and equally efficiently in any orientation. These four possible orientations include directing the circulating heated air exiting the furnace in either an upflow, downflow, horizontal-left, or horizontal-right direction.
Both the primary heat exchanger and the condensing heat exchanger include cells with channels formed therein to direct the flow of flue gas produced by combustion. These cells are positioned side by side in a parallel manner and are provided with a predetermined spacing to allow the blower air to flow around the cells. The blower air is heated by convection as it moves over the cells.
Gas is provided to the furnace by a gas manifold. Manifold orifices direct the gas into burners contained in a burner box and the gas is ignited as it exits the burners. The heated flue gas produced by combustion is then directed into the primary heat exchanger cells and induced to move therethrough. The channels provided in the primary heat exchanger cells eventually terminate at discharge ports. The discharge ports of the primary heat exchanger are typically aligned and secured in a first sheet metal panel.
The condensing heat exchanger of the multi-poise furnace is configured in a similar manner. A series of side by side condensing cells is provided. Each of these condensing cells has an inlet port for receiving the flue gas discharged from the primary heat exchanger and a pair of discharge ports. One of the pair of discharge ports being positioned below the other along the vertical when the furnace is installed with either the upflow or downflow orientation. When the furnace is installed with either a horizontal-left or horizontal-right flow orientation, the two discharge ports of each condensing cell are positioned side by side along the horizontal.
Proper functioning of condensing furnaces requires that the water vapor existing in the combustion products carried in the flue gas is condensed only in the condensing heat exchanger cells and not elsewhere within the furnace. Each condensing heat exchanger cell is designed to allow proper drainage out of at least one of the discharge ports in any one of the four possible installation orientations. In the upflow or downflow installations, the lower of the two discharge ports will function to drain the condensate formed within each cell, while both discharge ports of a given pair will function to drain the condensate from a respective cell when the furnace is installed with either the right-horizontal or left-horizontal flow orientations.
The collector box is positioned on the discharge side of the condensing heat exchanger. As noted above, condensate formed in the condensing cells will drain into the collector box. The collector box is provided with two drain taps so that the collector box may be properly drained of condensate. The drain taps are positioned in diagonally opposed corners of the rectangular front face of the box. In any one of the four possible installation orientations, one of the two drain taps will be positioned in the lower portion of the collector. Upon installation, this lower drain tap is connected by tubing to suitable drain piping including a trap. As the condensate level increases during the operation of the furnace, it will eventually reach the level of the lower drain tap and be removed through the tubing and trap into the drain.
During operating of the multi-poise condensing furnace, pressure within the channels of the heat exchanger cells and the collector box is increased above ambient by operation of an inducer mounted on the front of the collector box that induces flow of flue gas through the cells. Pressure within the channels and the box is also contributed to by combustion occurring at the inlet side of the primary heat exchanger.
A pressure switch is provided in the multi-poise condensing furnace to provide an added level of safety in operation of the furnace. This safety pressure switch is connected by tubing to one of two pressure taps provided on the front side of the collector box. The location of each of these pressure taps is proximate to a corresponding drain tap positioned along an arc between the horizontal and vertical of the ninety degree angle forming each of the diagonally opposed corners of the collector box. This location of the pressure taps is optimum because it places a pressure tap just slightly above the corresponding lower drain tap in any one of the four possible installation configurations. This particular position of the pressure tap is necessary so as to allow the safety switch to be activated shortly after the drain first becomes blocked.
The condensate drain piping or drain could become blocked by any one of a number of possible causes. In this blocked condition, condensate would continue to build up in the collector box as well as in the condensing heat exchanger in the event the furnace were to continue to operate. To avoid this possibility, a safety pressure switch, as described above, is connected to the pressure tap proximate to the lower drain tap. Thus, when the condensate level in the box raises above the drain tap because of some blockage, the condensate will shortly thereafter also block the pressure tap connected to the safety switch. The safety switch will detect this pressure drop in the line and then prevent further operation of the furnace until the blockage is cleared and proper drainage resumes.
In the typical installation, the upper pressure tap is fluidly connected to the upstream side of the drain trap. The pressure in the collector box is thus used to assist in forcing a steady flow of condensate through the drain piping to aid in preventing blockage in the drain. In some installations, it has been observed that splashing of condensate within the collector box near the lower pressure tap connected to the safety pressure switch will repeatedly activate and deactivate the switch thus turning the furnace off and on even though the furnace is experiencing proper drainage from the box. This nuisance splashing may be caused by vibration of the operating furnace or any one of a number of possible causes.